1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display device and its driving method that are capable of improving an aperture rate of an overall panel and its luminance.
2. Description of the Background Art
Recently, various flat type display devices are being developed to reduce a weight and a volume of a cathode ray tube (CRT). Such flat type display devices include a liquid crystal display, a field emission display (FED), a plasma display panel, an electro-luminescence, or the like. In order to improve a display quality of the flat type display devices, researches are being actively conducted to heighten a luminance, a contrast and a colorimetric purity.
Among them, the FED is divided into a tip type FED in which electrons are emitted by using a tunnel effect by concentrating a high electric field to an acute emitter, and a flat type FED in which a high electric field is concentrated to a metal with a certain area to emit electrons.
In the tip type FED, electrons are emitted from a conic protrusion portion made of silicon (Si) or molybdenum (Mo) by applying a voltage to a gate electrode to apply an electric field to an electron emission portion.
In the flat type FED, a stacked structure including a metal layer, an insulation layer and a semiconductor layer is formed, wherein electrons are injected into and passes from the metal layer and then emitted outwardly from an electron emission unit.
In the tip type FED, the electron emission amount is determined depending on characteristics of the emitter used for the electron emission. Therefore, every emitter should be fabricated uniform. In this respect, however, it is difficult to fabricate the emitters uniform with the current fabrication process, and in order to fabricate such an emitter, much process time is taken.
In addition, in case of the tip type FED, since the electrons are emitted from the acute emitter, scores of or hundreds of bolt should be applied to a cathode electrode and a gate electrode, causing a problem of much power consumption.
FIG. 1 is a view showing a cell of the flat type FED in accordance with a conventional art.
As shown in FIG. 1, each cell of the flat type FED includes: an upper substrate 101 on which an anode electrode 102 and a fluorescent material 103 are stacked; an electric field emission array 105 formed on a lower substrate 104; and a spacer 109 for supporting the upper substrate 101.
The electric field emission array 105 includes: a scan electrode 108 formed on the lower substrate 104; an insulation layer 107 formed on the scan electrode 108 and a data electrode 106 formed on the insulation layer 107.
The scan electrode 108 supplies current to the insulation layer 107, the insulation layer 107 insulates the scan electrode 108 and the data electrode 106, and the data electrode 106 is used as a fetch electrode for fetching an electron.
The space 109 is installed between the upper substrate 101 and the lower substrate 104. Since a high vacuum state is required between the upper substrate 101 and the lower substrate 104 (to prevent an arcing phenomenon due to an acceleration movement of electrons and a high voltage), the spacer 109 prevents a damage of the panel caused due to a difference between an internal pressure and an external pressure (the difference between an external atmospheric pressure and an internal high vacuum is equivalent to approximately scores of tones).
The flat type field emission display device in accordance with the conventional art constructed as described above will now be explained.
In order to display an image on the display device, first, a negative (−) scan pulse is applied to the scan electrode 108 and a positive (+) data pulse is applied to the data electrode 106. And, a positive (+) anode voltage is applied to the anode electrode 102.
Then, electrons tunnel the insulation layer 107 from the scan electrode 108 to the data electrode 106 and are accelerated toward the anode electrode 102.
The electrons collide with red, green and blue fluorescent materials 103 and excite the fluorescent material 103.
At this time, a visible ray of one of the red, green and blue colors is generated according to the fluorescent material 103.
Compared with the tip type FED, the flat-type FED can be driven at a low voltage since the scan electrode 108 and the data electrode 106 are installed in a facing manner with a certain area.
That is, only a few V to 10V is applied to the scan electrode 108 and the data electrode 106 of the flat type FED, and the scan electrode 108 and the data electrode 106 emitting electrons respectively have a certain area. Thus, compared with the tip-type FED, the scan electrode 108 and the data electrode 106 can be fabricated with a simple fabrication process.
FIG. 2 is a plan view showing a field emission display device in accordance with the conventional art.
As shown in FIG. 2, the FED includes: first and second data connection parts 202a and 202b for receiving a drive voltage from a data driving unit (not shown); a scan connection part 201 for receiving a drive voltage from a scan driving unit (not shown); an anode electrode 102 for receiving a drive voltage from an anode driving unit (not shown); and a connection part 204 for electrically connecting the anode electrode 102 and the upper substrate 101.
The first and second data connection parts 202a and 202b receive the drive voltage from the data driving unit and supply it to the data electrodes, and the scan connection part 201 receives the drive voltage from the scan driving unit and supplies it to the scan electrodes.
The anode electrode 102 is formed within an effective display part 203 of the upper substrate 101, and the anode driving unit applies a few kV high voltage to the anode electrode 102 typically formed as a thin film through the connection part 204.
FIG. 3 is a plan view showing the effective display part.
As shown in FIG. 3, the effective display part 203 includes red cells, green cells and blue cells which are sequentially disposed at regular intervals, and a spacer 109 between cells.
In order to form the spacer 109, a certain space is obtained between the cells. In the region where the space 109 is not formed, the areas between cells are the same each other. Reference numeral 301 denotes an emitter electrode and 302 denotes a fluorescent material 302.
The spacer 109 is divided into a rib type and a cross type. As shown in FIG. 4, there are installed hundreds and thousands of rib type spacers 401 to support a vacuum space between the upper substrate 101 and the lower substrate 104.
Thousands of cross-type spacers 501 as shown in FIG. 5 are installed to support the vacuum space between the upper substrate 101 and the lower substrate 104.
The rib-type and cross-type spacers 401 and 501 are installed between cells (R, G and B). Thus, the cells (R, G and B) are disposed adjacent with a certain space therebetween so that the spacers 501 and 501 can be installed therein.
However, in general, cells are disposed with the certain space (in consideration of formation of the spacer) therebetween, much space loss occurs. That is, since there should be a certain space even between adjacent cells with no spacer formed therebetween, an efficiency of a panel and an aperture rate are reduced.
In addition, since the electron beam is distorted according to the quantity and the position of the spacer 109 within the effective display part 203 (a phenomenon that a proceeding direction is changed as electrons collide with the spacer 109), the brightness of the adjacent cells differs and the angle at which an electron beam spreads is changed to cause a problem that there is a difference in the brightness of a screen.
Moreover, since scores of and hundreds of spacers 109 are formed within the effective display part 203, the aperture rate between the anode electrode 102 and an emitter (not shown) (area occupied by the fluorescent material over an overall area of one cell) is restricted. Therefore, with the disposal of the spacers 109, the aperture rate of the overall panel is degraded, and accordingly, a luminance and efficiency are low.